1. Field of the Invention
The invention relates to an ablation device for cardiac tissue, especially for forming a circular lesion in the region of a vessel orifice in the heart, comprising a catheter that is provided in the region of its distal end with an abutment device for holding the distal end of the catheter on a cardiac vessel orifice; and a linear ablation applicator that is disposed distally or proximally relative to the abutment device of the catheter and can be brought from a straight passive position into a radially expanded, approximately circular-arc-type encircling ablation position.
2. Background Art
Regarding the background of the invention it can be stated that catheter ablation is a therapy that is used to an increasing degree to treat certain types of arrhythmia. In the process, a lesionxe2x80x94i.e., a denaturation of tissue along the line of a tissue ablation or tissue scarringxe2x80x94is created with the aid of the ablation applicator of the catheter at a certain location in the myocardial tissue in order to sever the faulty electrical stimulus pathways at that location that are responsible for the arrhythmias. The introduction of energy into the myocardial tissue via the ablation applicator, as a rule, takes place by means ablation electrodes that operate with high-frequency current. Other forms of energy, such as microwave energies, high-energy direct current or, in principle, other denaturing mechanisms, such as freezing or chemicals (e.g., alcohol), may furthermore also be used for the ablation. The term xe2x80x9cablation applicatorxe2x80x9d, as it is used in the present application also in connection with the invention, shall always mean all of the listed ablation options, with ablation electrodes representing the most common variant.
From a multitude of ablation catheter variants that are adapted to their respective purposes, WO 98/49957 A1, which discloses an ablation device for generating linear lesions between the orifice openings of two pulmonary veins into the atrium of the heart, has been selected as the prior art. According to the disclosure of this reference, a steerable catheter is provided, which carries in front of its distal end an anchoring device in the form of a dilatable balloon to secure the catheter in the ostium of the pulmonary vein.
In this known ablation device the catheter serves not only for the basic positioning of the ablation applicator, but it also carries on its shaft the given ablation electrodes themselves. In this special design the catheter shaft can now be brought proximally relative to the ablation electrodes by means of a second guiding device to the front of the orifice opening of a second pulmonary vein so that the linearly aligned ablation electrodes come to rest on the connecting line between the two orifice openings of two adjacent pulmonary veins. In this manner a linear lesion can reliably be applied between the two orifice openings.
Further embodiments of ablation catheters are shown in, e.g., U.S. Pat. No. 5,239,999 A, WO 95/15115 A1 or WO 95/13111 A1, which disclose ablation electrodes in variably coiled or slightly bent shape.
Recent studies have shown that circular lesions around or at the orifices of the pulmonary veins (hereinafter: pv orifice) into the atrium have been successful, especially for treating the arterial fibrillation of the heart.
The known ablation devices are not practical for lesions of this shape, there being no or hardly any possibility of putting into practice an annular arrangement of the ablation electrodes around or at the pv orifice.
The invention thus has as its object to present an ablation device whereby a circular lesion around or at a vessel orifice in the heart can be formed in a manner that is reliable and with an application technique that is easy to perform.
According to the invention, a catheter with a linear ablation applicator is provided that is disposed distally or proximally relative to the abutment device of the catheter and can be taken from a straight passive position to a radially expanded, circular-arc-type encircling ablation position and is preferably displaceable axially relative to the abutment device.
The inventive further development of the catheter provides for the ablation applicator, by its encircling in the way of a circular arc in the ablation position, to be brought quasi shape-inherently into a correct position for applying the circular lesion and kept clean by the abutment device. A high degree of application reliably is thus attained in this manner, while accordingly improving the therapeutic success.
The ablation applicator is preferably disposed distally in front of the abutment device so that a lesion can be formed at the pv orifice.
The abutment device is preferably a dilatable balloon on the shaft of the positioning catheter. The diameter of the balloon in its inflated condition must exceed the diameter of the vessel concerned, i.e., it is in an order of magnitude of approximately 15 mm and more. By the aid of the catheter, the balloon is forced against the vessel wall area around the pv orifice, forming an abutment for the ablation applicator that lies distally in front of it. As a result, the ablation applicator can be held properly in the xe2x80x9cspandrel-typexe2x80x9d area between the balloon front and the pv orifice.
To aid in the creation of the circular-arc-type encircling ablation position, the ablation applicator is formed preferably by a multiple-electrode arrangement, the individual electrodes of which, which are aligned in the axial direction, are composed of a highly flexible materialxe2x80x94for example of one spiral winding per electrode, or of a flexible, conducting plastic.
A coverage of at least 180xc2x0 by the ablation applicator ensures that a completely closed circular lesion can be attained with only one rotation of the ablation catheter.
Even though this is not a direct object of the invention, it needs to be pointed out that the catheter may be provided with known measures for controlling its correct position. The position may, for example, be controlled sonographically by means of an ultrasonic transducer disposed at the tip of the catheter, or by means of a bipolar electrogram, which can be derived by means of a bipolar electrode arrangement at the tip of the catheter. The catheter may also incorporate additional lumen for injecting an X-ray contrast medium, which is injected via the lumen into the pulmonary vein for angiographic imaging.
Further characteristics, details and advantages of the invention will become apparent from the following description, in which embodiments of the object of the invention will be explained in greater detail based on the drawings.